Recent advances have yielded new and improved fluorescent light sources that effectively compete with incandescent and tungsten-halogen light sources and bulbs. Recent advances in electronic ballasts have yielded smaller and more reliable ballasts for use in lighting applications.
When designed for use with phase controlling triac type dimmers, an electronic ballast circuit must satisfy the requirements of the triac related to holding current requirements. The triac, when in its conducting state, must have the current magnitude above a minimum holding current to conduct current without undesired interruptions during the time of each half cycle of the AC power line voltage supply. Otherwise, the operation will result in undesired lamp flickering.
Compact fluorescent lamps (combined fluorescent lamp and electronic ballast) intended for operation from an ordinary AC power line typically include a full-wave rectifier, an energy storage capacitor, a high frequency inverter made with switching transistors and supplied by the energy storage capacitor, and a resonant circuit to start and operate the gas discharge lamp as the light source.
Prior art arrangements typically comprise a single stage electronic ballast with high power factor and with lower harmonic distortion of the current drawn from the AC power line that incorporate energy feedback from the output of the ballasts to the input. The feedback of energy from the output to the input as used in prior art products is designed in such a way to either satisfy the requirement of a triac holding current or to satisfy the full dimming range without visible flicker. The visible flicker is related to a ripple voltage present at the storage capacitor. The voltage ripple should be kept at minimum at all dimming levels. The light dimming range of the lamp and its relation to dimmer range is the result of the energy feedback, as well. The energy feedback is not self-adjustable and, in fact, provides increased energy feedback from the output to the input while dimming function is performed. This leads to undesired drop of frequency of operation of the self-oscillating inverter and create dangerous situation when the resonant circuit will have a capacitive impedance character which leads to destructive cross conduction of the of the switching transistors.
Unfortunately, numerous attempts have been made without success to develop an electronic ballast or other mechanism to enable fully dimmable compact fluorescent lamp operation.